A "caged" molecule is a photosensitive, but temporarily inert, precursor of a biologically active molecule. Absorption of light transforms the precursor into a molecule with full bioactivity. Because light can be easily focused and steered, and photochemical changes are fast, caged molecules represent a versatile tool for manipulating biology with light with high temporal and spatial control. The long-term objective of this project is to develop a broad spectrum of caged molecules that will allow cellular physiologists to use light to probe and control dynamic signaling processes in living cells and tissues. This proposal has four foci: 1) Develop new "cages" that have a) strong light absorption in single- and two-photon applications, b) high yield of product molecules upon photolysis, c) fast kinetics of product photorelease, and d) high pre-photolysis stability. 2) Develop new caged probes of neural signaling including neurotransmitters, lipid mediators, and inhibitors of transmitter transport. 3) Develop two new specific probes of intracellular calcium signaling: an optimal caged calcium and a caged agonist for the ryanodine receptor. 4) Apply the newly developed tools in ongoing and emerging independent and collaborative research to explore four topics in cellular neurophysiology: dendritic signal processing, synaptic plasticity, shaping of the synaptic event by glia, and calcium regulation of excitability.